An instruction prefetch buffer control (20) is provided for an instruction prefetch buffer array (10) which stores the code for a number of instructions that have already been executed as well as the code for a number of instructions yet to be executed. The instruction prefetch buffer control includes a register (201) for storing an instruction fetch pointer, this pointer being supplied to the buffer array (10) as a write pointer which points to the location in the array where a new word is to be written from main memory. A second register (205) stores an instruction execution pointer which is supplied to the buffer array (10) as a read pointer. A first adder (203) increments the first register to increment the instruction fetch pointer for sequential instructions and calculates a new instruction fetch pointer for branch instructions. A second adder (215) increments the second register to increment the instruction execution pointer for sequential instructions and calculates a new instruction execution pointer for branch instructions. Incrementing of the second register is variable depending on the length of the instruction. A third adder ( 221) is responsive to the output of the first adder and a branch target address to calculate whether the target instruction is contained in the array (10) and, if it is, causes the new instruction execution pointer calculated by the second adder (215) to be loaded into the second register (205).

Instruction prefetch buffer control

A random access memory having the capability to access one or more bytes in one or more memory word locations of a multi-byte memory array within one memory cycle. Variable length instruction and data words composed of multiple bytes are stored in a block of addressable locations in a memory so that individual bytes of each word are aligned in columns. Each column of bytes is addressable independently of the other byte columns via adders. A most significant bit portion of a memory location address is fed into a first input of column adders and the output of a first decoder circuit is fed into a second input of the adders for address incrementing within one memory cycle. A second decoder circuit generates a separate read or write enable line to each column of bytes. Both decoders are controlled by a least significant bit portion of the memory address and reference word byte size codes. A bi-directional multiplexer rearranges the order of the bytes so they appear in the proper order at the memory interface.

Byte addressable memory for variable length instructions and data

An interruptible microprogram sequencing unit (MSU) for providing a sequence of microinstruction addresses to a control memory containing microinstructions for the operation of a microprogrammed apparatus. The MSU includes an address output for providing microinstruction addresses to the control memory, an address bus connected to the address output such that a plurality of microinstruction addresses applied to the address bus are sequentially provided to the address output, means connected to the address bus for applying the plurality of microinstruction addresses to the address bus, an interrupt return register operably connected to the address bus for receiving a microinstruction address from the address bus and storing the received microinstruction address, and means connected to the address bus for interrupting the sequence of microinstruction addresses and effecting storage of a microinstruction address on the address bus in the interrupt return register.

Interruptible microprogram sequencing unit and microprogrammed apparatus utilizing same

A microsequencer includes a memory array (110) which is interfaced with a push/pop register (100). Data is input to the push/pop register (100) through a multiplexer (104) and also to Read register (102). The stack comprised of the RAM (110) and the register (100) can be push or pop with control logic (120). Stack pointer (130) and Read pointer (134) are provided for storing the stack and read pointers. The Read register (102) allows reading of data independent of the contents of the push/pop register (100) and the Read pointer (134) allows independent reading of information in the RAM (110).

Register stack for a bit slice processor microsequencer

A method and apparatus for updating the architectural state in a system implementing staggered execution with multiple micro-instructions. According to one aspect of the invention, a method is provided in which a macro-instruction is decoded into a first and second micro-instructions. The macro-instruction designates an operation on a pieced of data, and execution of the first and second micro-instructions separately cause the operation to be performed on different parts of the piece of data. The method also requires that the first micro-instruction is executed irrespective of the second micro-instructions (e.g., at a different time), and that it is detected that said second micro-instruction will not cause any non-recoverable exceptions. The results of the first micro-instruction are then used to update the architectural state in an earlier clock cycle than said second micro-instruction.

Method and apparatus for handling imprecise exceptions

A variable architecture digital computer to provide real-time control comations a for missile by executing efficient variable-length instructions optimized for such application by means of a microprogrammed processor and an instruction byte string concept.

H. Clifford Kancler

Papers

Variable architecture digital computer